In recent weeks, a friend of mine living in Emerald in Whistler has had her sleep (not to mention other activities) seriously disrupted by the nightly chorus of amphibians in her local wetland. The Sea to Sky corridor is home to four species of frogs and one species of toad.
The Columbia Spotted frog ( Rana luteiventris ) can be up to 10 cm in length, with females slightly larger than males. This dimorphism is common in most frog and toad species.
Another dimorphism in most species is that only the males are vocal; the male Columbia Spotted frog’s call is a weak 5-10 beat cluck, similar to the sound of a human clicking their tongue against the roof of their mouth.
The Wood frog ( Rana sylvatica ) can grow up to 5 cm in length, with the male’s sounds very much like the quack of a duck. The Pacific treefrog (Hyla regilla ) is up to 4 cm long. The mating call of the male is a loud krek-ek sound. Lastly the Coast Tailed Frog (Ascaphus truei) is only 3.5 cm from nose to rump and both sexes of this species are voiceless.
The only toad in our area is the Western toad (Bufo boreas ) with a length of up to 14 cm. Most toads, the Western toad included, have a kidney-shaped parotid gland behind each eye. This gland along with its warts, if it has them, is used to secrete a bitter, sticky substance to ward off predators. The male Western toad does not produce a mating call, but will emit a quiet, twittering release call‚ if they are accidentally grasped by another male during courtship.
The breeding seasons for our local frog and toad species occur sometime between February and June, the exception being the Coast Tailed frog who mates in the autumn. Most species of male frogs and toads have a distinct call to attract females of their species to the breeding area. The breeding area is usually the edge of a small, slow moving body of water or a wetland.
The male produces sound by passing the air from his lungs over the vocal chords to the vocal sacs. The vocal sacs act as resonators, amplifying the sound proportionally to their size. The vocal sacs of the Pacific treefrog amplify their call so loudly they can be heard up to 1.5 km away, whereas the Columbia Spotted frogs‚ call travels only 30 metres.
The male frogs and/or toads calling within a particular wetland create what is called a "chorus". The chorus usually occurs at night to avoid predation, but males will call during the day at the peak of the breeding season. The males can sense vibrations in the water created by approaching females, predators or even a strong breeze. These vibrations can cause individuals or even the entire chorus to stop calling while they determine what created it. When the frogs/toads are sure there is no threat they will begin calling/chorusing again.
During the time a male is calling he will remain totally sedentary so that the female can locate him. However if another male challenges him, he will defend the 50 cm territory around himself.
The ear of the frog or toad is called the "tympanum" and is the flat circle behind its eye. Because the female’s hearing allows her to best identify and locate the males of her species she is able to choose a partner, even in a noisy pond packed with numerous species of frogs and toads chorusing their hearts out.
Once the female frog or toad has located and chosen a partner, the male will climb onto her back and grasp her with his front legs. The female then lays her eggs into the water, while at the same time the male releases his sperm to fertilize them. This copulatory process is called "amplexus".
The number of soft, jelly-covered eggs released by the females varies by species; the Columbia Spotted frog produces 1,000-1,500 eggs, while the wood frog produces 2,000-3,000, the Pacific treefrog only between 10 and 70 eggs and the Western toad 5,000-16,000.
Coast Tailed frogs are so named because the male has what appears to be a "tail". In fact it is actually the copulatory organ, which he uses to fertilize the eggs of the female internally. Unlike the other local frog and toad species, this mating process occurs in early autumn and the female does not actually lay the string of 35-85 fertilized eggs underwater until the following summer. As the Coast Tailed frog does not mate at the same time of year as other species they do not require tympanums or vocalizations to hear and be heard in all the springtime racket.
Despite all the nightly noise at this time of the year, frog and toad populations in B.C. and world-wide are decreasing rapidly due mainly to habitat destruction. In fact, the Coast Tailed frog and the Western toad are currently deemed "species of special concern" on Environment Canada’s Species at Risk list.
To learn more about our local frogs and toads; how to identify them and to protect them visit BC Frogwatch at: http://wlapwww.gov.bc.ca/wld/frogwatch/whoswho/whoswho.htm
Monthly Bird Walk — The next bird walk will take place Saturday, May 1st. Join Whistler experts in the monthly update of our feathered locals and migrants.
Arbor Day — Join the Whistler Naturalists Saturday, May 11th between 9 a.m. and noon as we help reforest the north gravel pit in the Emerald Forest. We’ll meet at the gravel pit. It’s likely best to park on the shoulder of Alta Lake Road; look for the sign between Rainbow Trail and Alpine Meadows. Definitely bring gloves and, if possible, a trowel, shovel, or mattock. Post-planting family BBQ at Edgewater at 1 p.m. (bring your own cup).
Written by: Sorcha Masterson